Device for grinding and resharpening gear-cutting hobs



Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March 27,1963 5 Sheets-Sheet 1 WIIIIIIIIIII/ Dec. 7 1965 RIEBEL 3,221,447

F. DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March27, 1963 5 Sheets-Sheet 2 Dec. 7, 1965 F. RIEBEL DEVICE FOR GRIND INGAND RESHARPENING GEAR-CUTTING HOBS 5 Sheets-Sheet 5 Filed March 27, 1963Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March 2'7,1963 5 Sheets-Sheet 4 Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS 5 Sheets-Sheet 5Filed March 27, 1963 United States Patent Claims The invention relatesto a device for grinding and resharpening gear-cutting hobs,particularly hobs for cutting spur gears having a concave back. Thedevice operates with a profiled grinding wheel, whereby the backs areground by plunge feed in a dividing process.

Hitherto known hobs are resharpened by regrinding the tooth face. Herebythe whole back wear must be eliminated in peripherical direction. Fromthis results a tooth which is relatively long in peripherical direction;or, in other words, a long tooth pitch results. This tooth pitch means alow number of teeth of the hob which limits the speed of feed whencutting gears. The speed of feed does not only depend on the number ofthe teeth of the gear being cut, but also on the number of teeth of thehob. Furthermore, the number of resharpenings is relatively small inspite of the considerable tooth pitch. Both facts result in a loweconomy of cutting gears.

The purpose of the present invention is to provide a novel devicesuitable both for manufacturing hobs of the kind described, and forsharpening said hobs; a greater number of teeth are realized in thismanufacturing method while a greater number of resharpenings areachieved by means of the same device.

The purpose of the invention is attained by providing hob backs formedas surfaces of rotation which are concave with respect to the hob axisand are generated by a plunge feed by means of a profiled grinding wheelin a dividing process.

In the known relief grinding process the hob rotates while it is groundso that very small grinding-wheel diameters only are possible. Therelief grinding process is, therefore, uneconomical for resharpening.

The improved method used with the device according to the invention,however, admits grinding-wheel diameters which are greater, in mostinstances, than the diameters of the hobs. The grinding wheels may begiven diameters which are multiples of the respective hobs. Thesegrinding wheels have a long dressing life and make it possible to employthe same process for resharpening as for the original manufacturing ofthe hob back. When resharpening the back, the short side of the backwear is eliminated in radial direction. This gives to 6 times moreresharpenings per unit of length and when resharpening the tooth face.

By resharpening the hob back in radial direction an improved hob isachieved, the novel feature of which is that the teeth are so short inperipherical direction as safety considerations against breakage willallow. These improved hobs have 60 to 100% more teeth than the knownrelieved hobs.

A device according to this invention, adapted for grinding andresharpening the improved hobs, comprises means by which the profiledgrinding wheel plunges into or attacks the hob or, the hob is made toplunge into the wheel. The device further comprises a dividingattachment coordinated with the hob, and a swivelling base by which thehob axis can be inclined with respect to that of the profiled grindingwheel in correspondance with the helix angle of the hob. The device mayalso comprise a carriage combined with means for generating a lead, themotion of which is derived from the dividing attachment so that everydividing motion of the hob results in a translation between the hob andthe grinding wheel.

It is particularly economical if all teeth lying at the same flute areground simultaneously with a multi-profile grinding wheel.

The inventive device is adapted to provide a novel hob, for example forcutting spur gears, which shows improved features when compared toconventional relieved hobs having a constant tooth profile. It will beunderstood that in the present specification spur gear is mentioned inan exemplary fashion only and is meant to represent any gear adapted tobe machined by means of the cutting hobs here described.

The new device according to the invention provides a method ofmanufacturing hob backs by respective plunging of the profiled grindingwheel into the hob or vice versa, the axis of the grinding wheel beinginclined with respect to that of the hob by an amount corresponding tothe helix angle of the hob.

The invention also provides a device for resharpening the hobs madeaccording to the above-mentioned method, performed by the same processso that the hob-back wear is eliminated in radial direction while agrinding on the tooth face only serves for the smoothing thereof. Aftertwo or three resharpening processes an amount of material is removedwhich is smaller in peripheral direction than the back wear in the samedirection.

The invention provides a device adapted for making hob backs, andalternately for resharpening them, according to the methods outlinedhereinabove, so as to obtain novel hobs as described hereinabove.

The invention will now be more fully explained, together with otherobjects and many of the attendant advantages, as the same becomes betterunderstood by reference to the following detailed description, whenconsidered with the accompanying drawings, in which:

FIG. 1 shows a gear-cutting hob in lateral view and the generatingprocess of the hob back;

FIG. 2 shows the cooperation of the profiled grinding wheel and the hobon an enlarged scale;

FIG. 3 is a modification of the arrangement shown in FIG. 2;

FIG. 4 shows the grinding of a hob by means of a multiprofile grindingwheel;

FIG. 5 shows on an enlarged scale, a hob tooth and schematically themethod of resharpening;

FIG. 6 is the view of the tooth face of the hob shown in FIG. 5;

FIG. 7 shows a hob-grinding device according to the invention in a sideview;

FIG. 8 shows the device of FIG. 7 in a top view;

FIG. 9 shows the hob carriage in a top view and the dividing spindlestock in section; and

FIG. 10 shows the dividing plate and the change gears of the dividingspindle stock (view taken upside down from the side of the deviceopposite that shown in FIG. 7).

While the inventive device for grinding and resharpening gear-cuttinghobs will be fully described with reference to FIGS. 7 through 10, theimproved hobs, as well as some of the considerations that apply in theirprocessing, are being explained first, with reference to FIGS. 1 through6.

FIG. 1 shows, as an example, a gear-cutting hob 10 having teeth 11 whichare gound at their backs 12 by means of a profiled grinding wheel 13.This wheel is used both during the first production and during eachresharpening. The grinding wheel may perform a plunge feed in differentdirections, e.g., as shown by the arrows 14$, 15, 16. The extremedirection 14 is parallel to the tangent plotted against the back 12 atthe outermost sectional point A of the tooth edge. The outer extremedirection 15 is determined by the top K of a neighboring tooth 11a.Between these two extreme values all directions lying within an arc 17are possible, such as, for example, shown at 16. The direction 16 is thebase for the construction of the grinding device shown in FIGS. 7-10.The inclination of the profiled grinding wheel is indicated by aprojection 18 of the grinding wheel axis in the plane of FIG. 1.

FIGS. 2 and 3 show in partial sectional views, as a matter of example,two types of cooperation between hobs 21, 31 and respective grindingwheels 24, 33. According to FIG. 2, the root of the hob tooth has agroove at 22 and the grinding wheel 24 is formed so that only the flanks23 and the head 25 of the same tooth are machined with the grindingwheel 24. In the example according to FIG. 3, the flanks 32 of a spacebetween two hob teeth are ground simultaneously with the tooth root 34and the tooth heads of an appropriately profiled grinding wheel 33.

FIG. 4 shows the machining of a hob 41 with a multiprofile grindingwheel 42. Hereby a resharpening time is attainable which is even shorterthan the time needed for the conventional resharpening at the toothface. This method, however, can be employed only with relatively shorthobs and with a small helix angle. Otherwise the difference between theclearance angle of a tooth on one end of the flute becomes too great ascompared with that on the other end, because of the inclination of thegrinding wheel. In this case, the dressing of the grinding wheel must beperformed with a template and a diamond; the dressing plane must havethe same position with regard to the grinding wheel as the tooth facesof the teeth being ground simultaneously.

With FIG. the method of resharpening is described. AC and GH are thetraces of the hob back in the respective planes YY and X-X of thecutting points A and G (FIG. 6). The wear of the back appears in FIG. 5as the triangle ABD. If this hob were resharpened on the tooth face, theamount DB would have to be ground away, which is not economic. By theresharpening method exercised with the device according to theinvention, however, only the small amount AD is to be ground away inradial direction, and the above-mentioned lines AC and GH which are toshow the back appear as dotted lines EF and IL.

The tooth face may be smoothed by a slight grinding. Mostly it issufiicient to grind the tooth face at every second or third resharpeningof the hob back. OMNP is the tooth at the end of the hob life span.Regrinding of the tooth face will maintain the length of the tooth head(AC-MN) while the flute becomes deeper.

Both FIGS. 1 and 5 show clearly the difference in the constructionalfeatures between the improved hobs processed with the device accordingto the present invention and the known, relieved hobs having a constanttooth profile; i.e., the pitch (arc AK) which is very short as comparedto the cutting-profile depth (AG in FIG. 5) and the hob diameter; theteeth which are short as compared to the flute; and the backs which areconcave surfaces of rotation (AC and GH in FIG. 5).

The improved hobs with a pitch similar to FIGS. 1 or 5 always out withat least two teeth simultaneously in one thread, one behind the other.Contrary to the chattering manner in which a known hob with a long pitchworks, the short pitch of the improved hob results in very smoothcutting. The cutting edges are spared so much that, for example, if animproved hob with twenty teeth is made to cut with double the fed as aknown hob with only ten teeth, the number of workpieces being cut perresharpening is greater than that with a known hob, and mostly amountsto the double in case of stable workpieces.

In FIGS. 7-10 the inventive grinding device is shown which is adaptedboth for the manufacturing and the resharpening of the improved hobs.The feed means by which the profiled grinding wheel 13 plunges into thehob It), is a carriage slide 53 which is supported by rollers, as shownat 57. By a tension spring 58, carriage 53 is pressed hand against astop 59 during grinding so that the hob will have a good run-out. Theplunge feed motion is provided by an eccentric disc 60.

An adjusting slide 52 is connected with carriage 53, which carries anattachment 49 for the grinding wheel 13. By means of a hand wheel 77 andspindle screw 78, the grinding wheel 13 is set into the grindingposition as shown in FIG. 7 or into the opposite direction away from thehob 10, Where it is profiled by means of a crushing roll 54, theattachment 55 of which is directly mounted on the bed 56. For thecrushing process, belts '75 and 76 for grinding wheel 13 and disc 60,respectively, have to be inactivated, e.g. by disconnecting one endthereof. If conventional steel crushing rolls are used, wheel 13 doesnot have to be rotated because it is entrained by driven roll 54. Motors85 and 86 are provided for driving the grinding wheel 13 and theeccentric disc 60, respectively, through the afore-mentioned belts.FIGS. 7 and 8 also illustrate a belt 76' for driving roll 54 from motor86.

FIGS. 8-10 show that the hob 10 is set up on an arbor between atailstock center 79 and a dividing spindle 69. The dividing motion isexecuted as soon as the carriage 53 gives an impulse, upon reaching theback dead center. This is accomplished by a switch 62. which closes acircuit (not shown) so that a solenoid 63 retracts an indexing finger 64from a notch of a dividing plate 65. A motor 66 turns the dividingspindle 69 and the plate 65 by means of a drive comprising a worm 67 anda worm wheel 68. As soon as carriage 53 leaves the back dead center,solenoid 63 is de-energized whereupon finger 64 is urged by a spring(not shown in detail) against the outer diameter of the dividing plate65, and it falls into the next notch.

By means of change gears 70 the rotation of the dividing spindle 69 istransmitted to a lead screw 72 which displaces a top carriage Stl withrespect to a carriage rest 73 from one tooth to the next in accordancewith the lead of the hob 10.

By means of a swivelling base 71 (see FIG. 9), the axis of the hob 10can be inclined in relation to the axis of the grinding wheel,corresponding to the helix angle of the hob.

To adjust the clearance angle, the hob can also be adjusted with regardto the grinding wheel 13, perpendicular to the direction of the plungefeed (performed by carriage 53), by means of a vertical slide 74 and aspindle screw (FIG. 7).

The grinding device may also be employed for grinding and forresharpening of profile cutters and other similar tools.

It should be understood, of course, that the foregoing disclosurerelates only to a preferred embodiment of the invention and that it isintended to cover all changes and modifications of the example describedwhich do not constitute departures from the spirit and scope of theinvention as set forth in the appended claims.

What is claimed is:

1. A device for manufacturing and sharpening gearcutting hobs in adividing process by means of profiled grinding wheels, the hobs having aplurality of cutting teeth arranged in a helical pattern around the hobperiphery in at least two substantially adjacent rows and tooth backsforming concave surfaces of rotation with respect to the axis of thehob, comprising, in combination, support means for a hob to be machined,dividing attachment acting on said hob support means for rotating thesame tooth by tooth, support means for a profiled grinding wheel,swivelling means acting on said hob sup port means for tilting the axisof said hob with respect to that of said grinding wheel, feed meansacting on said wheel support means for producing plunge feed betweensaid hob and said grinding wheel, and means for generating a lead actingon said hob support means for displacing the same longitudinally fromone row of teeth to the other.

2. A device according to claim 1, further comprising drive means forsaid dividing attachment, the motion of said lead generating means beingderived from said drive means.

3. A device according to claim 1, wherein said hob sup port meanscomprises a movable carriage, a tailstock center and a dividing spindle,the latter being operatively connected with said dividing attachment.

4. A device according to claim 1, wherein said dividing attachmentcomprises gear means and indexing means operatively connected therewith.

5. A device according to claim 4, further comprising electrical meansfor actuating said indexing means depending on the position of said leadgenerating means.

6. A device according to claim 5, further comprising contact meansadapted to disengage said indexing means in the position of said wheelsupport means remotest from said hob support means.

7. A device according to claim 1, wherein said wheel support meanscomprises a movable attachment for rotatably supporting said grindingwheel, biasing means for urging said attachment toward said hob supportmeans, and adjustable stop means for limiting the movement of saidattachment in the position of said wheel support means closest to saidhob support means.

8. A device according to claim 1, wherein said swivelling meanscomprises a carriage rest and a carriage movable thereon for incliningsaid hob with respect to said grinding wheel by an amount correspondingto the helix angle of said hob.

9. A device according to claim 1, wherein said feed means comprises aneccentric drive operatively connected to said wheel support means forproducing plunge-type reciprocation with respect to said hob supportmeans.

10. A device according to claim 1, wherein said lead generating meanscomprises a lead screw the motion of which is derived from said dividingattachment, every dividing motion of said hob resulting in a translationbetween said hob and said grinding wheel.

11. A device for grinding and resha-rpening gear-cutting hobs in adividing process by means of profiled grinding wheels, the hobs having aplurality of cutting teeth arranged in a helical pattern around the hobperiphery in at least two substantially adjacent rows and tooth backsforming concave surfaces of rotation with respect to the axis of thehob, comprising support means for a hob to be machined, support meansincluding a movable attachment for rotatably supporting a profiledgrinding wheel,

the diameter of said wheel being approximately twice that of said hob,feed means for producing plunge feed between said hob and said wheel,biasing means for urging said attachment toward said hob support means,and adjustable stop means for limiting the movement of said attachmentin the position of said wheel support means closest to said hob supportmeans.

12. A device for grinding and resharpening gear-cutting hobs in adividing process by means of profiled grinding wheels, the hobs having aplurality of cutting teeth arranged in a helical pattern around the hobperiphery in at least two substantially adjacent rows and tooth backsforming concave surfaces of rotation with respect to the axis of thehob, comprising support means for a hob to be machined, support meansincluding a movable attachment for rotatably supporting a profiledgrinding wheel, the diameter of said wheel being approximately twicethat of said hob, feed means for producing plunge feed between said hoband said wheel, dividing means for rotating said hob tooth by tooth, andmeans for generating a lead for displacing said hob longitudinally fromone row of teeth to the other, said dividing means and said generatingmeans acting both on said hob support means.

13. A device for grinding and resharpening gear-cuttin-g hobs in adividing process by means of profiled grinding wheels, the hobs having aplurality of cutting teeth arranged in a helical pattern around the hobperiphery in at least two substantially adjacent rows and tooth backsforming concave surfaces of rotation with respect to the axis of thehob, comprising Support means for a hob to be machined, support meansincluding a m-ovable attachment for rotatably supporting a profiledgrinding wheel, the diameter of said wheel being approximately twicethat of said hob, feed means for producing plunge feed ber tween saidhob and said wheel, and means for journaling said wheel and said hobwith their respective axes arranged substantially parallel to oneanother.

References Cited by the Examiner LESTER M. SWINGLE, Primary Examiner.

13. A DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS IN ADIVIDING PROCESS BY MEANS OF PROFILED GRINDING WHEELS, THE HOBS HAVING APLURALITY OF CUTTING TEETH ARRANGED IN A HELICAL PATTERN AROUND THE HOBPERIPHERY IN AT LEAST TWO SUBSTANTIALLY ADJACENT ROWS AND TOOTH BACKSFORMING CONCAVE SURFACES OF ROTATION WITH RESPECT TO THE AXIS OF THEHOB, COMPRISING SUPPORT MEANS FOR A HOB TO BE MACHINED, SUPPORT MEANSINCLUDING A MOVABLE ATTACHMENT FOR ROTATABLY SUPPORTING A PROFILEDGRINDING WHEEL, THE DIAMETER OF SAID WHEEL BEING APPROXIMATELY TWICETHAT OF SAID HOB, FEED MEANS FOR PRODUCING PLUNGE FEED BEBTWEEN SAID HOBAND SAID WHEEL, AND MEANS FOR JOURNALLING SAID WHEEL AND SAID HOB WITHTHEIR RESPECTIVE AXES ARRANGED SUBSTANTIALLY PARALLEL TO ONE ANOTHER.